The present invention relates to the locating of concrements in the body of living beings for purposes of determining where the focal point of a shock wave reflector right has to be positioned so that it may comminute the concrement, and more particularly the invention relates to a system for locating concrements under utilization of X-rays in combination with an ultrasonic device.
German patent No. 23 512 47, see also U.S. pat. No. 3,942,531, discloses a device for the comminution of concrements inside the body of a living being, under utilization of a focusing chamber which is a portion of a rotational ellipsoid, having two focal points. In one focal point a spark discharge produces a highly concentrated point like shock wave which propagates in all directions, is reflected by the focusing chamber and refocused in the second focal point of this ellipsoid. That second point must be positioned such that it coincides with the concrement. The comminution of kidney stones without operative invasion and without introduction of probes or the like into the body has been successfully practiced with this technique. An extensive description of equipment and therapeutic procedure is for example found in "Extra corporal shock wave lithotripsy", Ch. Chaussy ed Munich 1982.
Before this shock wave comminution process can take place, it is necessary to very accurately determine the location of, for example, the kidney stone, so that the focusing chamber can be positioned for purposes of having its second focal point as defined above coincide with the kidney stone. For this one has used for example two X-ray systems, which operate basically, on the principle of triangulation and are oriented to obtain particular axes of observation that will pass through the concrement and from the orientation of the X-ray system and their respective axes one can then determine the location of the kidney stone vis-a-vis the X-ray system. The focusing chamber is then positioned accordingly.
Obviously intensive exposure of the patient to X-rays have to be avoided so that the number of X-ray images taken should be limited Nevertheless, the known locating method is tied to two X-ray systems. Following the locating of the kidney stone which in turn is followed by positioning of the focusing chamber, the kidney stone is comminuted by the shock waves to obtain a very fine grit, which is discharged from the body by natural process.
The German patent No. 27 22 252, suggests a device for locating concrements by means of ultrasonics. Satisfactory results for this approach presupposes that the stone and the organs around it have a fixed, resting position. However certain inherent motion of the stone and of the organ in which the stone is lodged, for example on account of breathing will cause the stone to move in and out of the plane of ultrasonic locating. Therefore, the ultrasonic image will change continuously and the stone can be identified only for a very short period of time, namely when it passes through the locating plane to which the ultrasonic imaging system adjusted.
As the focusing chamber is positioned so that its second focal point as mentioned above, is made to coincide with a point in the imaging plane, super imposed oscillatory motion of the stone, may in fact destroy the locational information about the position of the stone and the entire locating procedure may have to be repeated. This process is particularly time consuming if the positioning of the concrement, for example by shifting the patient in relation to a particularly adjusted and positioned focusing chamber is carried out independently from the concrement locating device, i.e. if there is no follow-up control involved. A more suitable tracking device is suggested by one of us and others of copending patent application now issued as U.S. Pat. No. 4,669,483.